The present invention is an Insulation Displacement Connector (IDC) for use with multi-conductor cable, such as Flat Flexible Cable (FFC) and Flexible Printed Circuits (FPC) which would provide the same convenience, cost savings, and long-term reliability that has been available for solid conductor round wire connections using the “U” form contact for over two decades. The result is a design that successfully translates IDC technology used for round wire interconnects to flat conductor systems.
The “U” form IDC contact was originally developed for the telephone industry to terminate solid and stranded core, round conductor wire. In these connectors, “U” shaped metal contacts are used to both pierce through and displace the insulation to make a gas-tight contact with the underlying conductor(s) of either a single conductor round wire or multi-conductor laminated round wire cable.
Application of an IDC for use with multi-conductor cable can result in a significant cost savings. With current connectors, the conductors of the multi-conductor cable must be exposed in the area that the interconnection will be made. Some connectors require exposure on both sides and others require either the addition of a stiffening film to the backside of the cable in the connector area or holes punched in the cable for positioning and strain relieving. The end user must specify and purchase the multi-conductor cable at specific lengths with the exposed areas either punched or laser cut and the holes either punched or drilled. Each of these operations has a cost and tolerances associated with it. Failure to meet the tolerances will result in rejected product, lost time, and lost money. With an IDC, exposing the conductors before assembly is not required and an assembler can simply use continuous lengths of multi-conductor cable that can be cut to length without any special tooling.
Until now, there have been few applications for this technology for flat conductor cables. Previous IDC connector designs have attempted to translate the technology used for round wire to flat conductor cable but have included severe limitations. FIG. 1 shows an example of an IDC connector attempting to use round wire technology for flat conductor cable connectors.
One such limitation is that the contact pierces through the insulation on both sides of the cable. This limitation has several inherent problems. The first problem is that the insulation distance or “spacing” between the conductors has been decreased. A decrease in spacing will reduce the high-voltage carrying capacity of the system and may cause short circuiting failures. The second problem is that piercing through the insulation weakens it, and may cause it to tear and expose an air gap between adjacent conductors, also decreasing the high-voltage carrying capacity of the system. This problem would especially cause concern when using polyimide insulation materials, which have a lower tear resistance than polyester materials.
Another problem emerges when the copper conductor is folded during the engagement of the contact and the conductor. Since copper is a ductile material, it does not provide enough spring resistance and will create an unreliable electrical contact as the copper relaxes over time and reduces the contact pressure at the connection point. Also, if the conductor does not fold, it will be either damaged or broken. Also, its current carrying capacity will be decreased.
A large part of the IDC market for flat conductor cable is the crimped-on contact style. This connection system uses contacts, which are individually crimped onto the conductors of the FFC/FPC and then may be inserted into a connector housing or soldered directly to a PCB. There are various designs for this type of contact. One of these types pierces through both the insulation and the copper conductor, which damages the conductor and reduces its current carrying capacity. Another design pierces through the insulation between the conductors and wraps around the conductor to provide pressure against small lances that pierce the insulation to make contact with the conductor. FIG. 2 shows this type of crimped-on contact.
As previously described, the piercing of the insulation both reduces the spacing between conductors and weakens the insulation, which may tear. Both of these designs rely on the forming of the crimped contact to provide the spring force necessary to maintain a gas-tight electrical contact. If the crimping process is not performed properly and consistently, the contact system will be unreliable. Also, this type of connection leaves the conductive material of the contact exposed on the outside of the cable with only an air gap to provide electrical insulation between the conductors, limiting the high-voltage carrying capacity of the system.
A fourth problem is that in many of these designs the contacts either intentionally or unintentionally may pierce through both the protective surface plating and copper conductors of the multi-conductor cable. Motion at the connection points may expose this copper to the environment and copper oxides may form which will propagate and eventually contaminate the connection causing a short or open circuit failure.
With all of the above-described designs, the conductor density is severely limited due to the space required to provide a contact that is sufficiently strong to provide the minimum contact force for a gas-tight connection. Many of these designs require a large spacing between the conductors and are not capable of being used in newer system designs, which require much higher density connectors.
Finally, previous IDC designs for multi-conductor cables always provided minimal contact area. The various IDC designs either piercing or bending the conductors used the side of the conductors to establish a contact area. Since the conductors in multi-conductor cables are generally flat, meaning the conductors are wider than they are deep, using the side of the conductor to establish a contact area reduces the prospective size of the contact area. A better IDC design would use the wide portion of the conductors thereby increasing contact area. Increased contact area means increased current flow capacity. Also, the multi-conductor cable density is impaired by the required piercing of insulation between conductors instead of making contact with the conductors on their wider surface.